Synergistic effects of coumarin and cis-2-butene-1,4-diol on high speed electrodeposition of nickel

The individual and synergistic effects of coumarin and cis-2-butene-1,4-diol on the surface morphology and the crystal structure of Ni electrodeposits at a high cathodic current density were investigated using SEM, XRD, SIM and electrochemical analyses. While the rough Ni layer composed of spiral-type deposits was deposited from an additive-free bath, the electrodeposits with a smooth and bright surface were prepared from the coumarin-containing bath. XRD analysis and the cross-sectional observation suggested that coumarin promotes the large columnar growth of Ni crystallites along [200] directions, resulting in the production of a highly leveled electrodeposition layer. In contrast, cis-2-butene-1,4-diol showed strong grain refining effects on the Ni electrodeposition by the suppressive effects on the every mode of the crystal growth except [220] orientation, resulting in a significant promotion of the Ni crystal nucleation. When both coumarin and cis-2-butene-1,4-diol were contained in the bath, highly smoothed Ni electrodeposits were deposited by the synergistic effects of the additives.